Networking
CSCI N321 – System and Network Administration
Copyright © 2000, 2012 by Scott Orr
and the Trustees of Indiana University
Section Overview
TCP/IP Basics
TCP/IP Configuration
TCP/IP Network Testing
Dynamic Host Config Protocol (DHCP)
Wireless Networking
References
CQU 85321 System Administration Course
 Chapter 15
TCP/IP Protocol Stack
Application (FTP, HTTP, DNS)
Transport Layer (TCP,UDP)
Network Layer (IP)
Link Layer (Device Drivers)
Physical Layer (media)
TCP/IP Packet Encapsulation
Service
Data
TCP/UDP
IP
Ethernet/PPP
UTP/PSTN
E
T/U
Data
IP T/U
Data
IP T/U
Data
E
Connecting to a Network
Hostname and IP Address assignment
Configuration of hardware
Default route (gateway) assignment
Name Service Configuration
Testing and troubleshooting
Hostnames
Uniquely identifies each system
Fully Qualified Domain Name
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hostname.site.domain[.country]
Country: 2 letter identifier for country
Domain: Type of site (edu, com, org)
Site: Unique name of organization
Hostname: Unique name of system
hostname: Display or set system name
IP Addresses
Unique for each connection (interface)
Consists of 4 octets (#.#.#.#)
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Network portion
Host portion
Special Addresses
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Network Address
Broadcast Address
IP Address Classes
Class
A
B
C
1st Byte
0 – 126
128 – 191
192 – 239
D
E
224 – 239
240 – 254
Format
Total Hosts
N.H.H.H 16 Million
N.N.H.H 64 Thousand
N.N.N.H 254
-
(Multicast)
(Experimental)
Subnet Masks
Splits networks into subnetworks
Separates address into 2 parts
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1’s – Network Portion
0’s – Host Portion
Example: Class C Network
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Address: N.N.N.H
Mask: 255.255.255.0 (255 = 11111111)
CIDR Notation: N.N.N.H/24
Interface Configuration
Hardware to connect to network
Common interfaces
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Ethernet
Modem
Loopback (lo) Interface
ifconfig – View/Configure interface
ipconfig – View interface (Windows)
Ethernet Addressing
Assigned by manufacturer (hardware)
Must be absolutely unique
Address format
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6 octets in hex (#:#:#:#:#:#)
First 3 octets: Manufacturer Identifier
Last 3 octets: Card serial number
Used for local network communication
Address Resolution Protocol
Translates IP addresses to Ethernet
(MAC) addresses
Who is 10.0.0.3?
I am (1:2:3:7:8:9)
10.0.0.1
10.0.0.2
10.0.0.3
arp –a: View the cache
10.0.0.4
Default Gateways
Connects Networks together
If destination not on local network,
packets sent through gateway
route: Display/configure routing
RedHat Network Files
/etc/sysconfig/network
HOSTNAME
GATEWAY
/etc/sysconfig/network-scripts/
ifcfg-[interface]
BOOTPROTO
IPADDR
USERCTL
NETWORK
ONBOOT
NETMASK
BROADCAST
ifup/ifdown [interface]
Name Services
/etc/hosts
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Local configuration
Localhost – 127.0.0.1
/etc/resolv.conf
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Domain Name Service (DNS) lookup
search: domains to search if not FQDN
nameserver (3): Nameservers to consult
/etc/nsswitch.conf
DNS Name Resolution
Root Server
Non-Recursive
2
3
1
4
5
Recursive
8
host.domain.com
7
dns.domain.com
6
dns.iupui.edu
dns.cs.iupui.edu
Network Testing
Localhost reachability
Hostname reachability
Local network reachability
Internet network reachability
DNS resolution
Network tools
ping – Reachability test
traceroute – Routing performance
netstat – Network performance stats
tcpdump – Packet sniffing
nslookup/dig – DNS Queries
Configuration tools (already discussed)
Dynamic Host Config Protocol
Client broadcasts a request for an IP
address and network information
Server leases address to client
Lease must be renewed periodically
Easy to make global network changes
Linux: BOOTPROTO=dhcp
Windows Networking
Windows CLI
ipconfig – Display Interface Settings
ping – Destination reachability
tracert – Router hops to destination
netstat – Performance statistics
nslookup – DNS lookups
route – Set/Display gateway
netsh – Change Interface Settings
netsh Examples
Display Interfaces
netsh interface show interface
Configure Interface
netsh interface ip set address \
local static [ip-addr] [netmask] \
[default-gw] 1
DNS Server Setting
netsh interface ip set dns local \
static [ip-addr]
Wireless Networks
Extend the network
Included in many devices now
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Laptops
Smart Phones
DSL/Cable Modems
Bandwidth (YMMV!)
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802.11b – 11 Mbps
802.11g – 54 Mbps
802.11n - 150/300/450/600 Mbps
Set Service Identifier (SSID)
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Shared “key” between clients and Access Point (AP)
Automatically detected vs. assigned
Wireless Security Issues
Sniffing / War Driving
Bandwidth stealing
Access to private resources
Security Measures
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Non-broadcasting SSIDs
MAC Access Control Lists (ACLs)
WEP????
WPA/WPA2
RedHat ifcfg- Additions
TYPE=Wireless
ESSID=[ssid name]
CHANNEL=[1-11]
MODE=[Auto|Managed|Ad-hoc]
Can set manually with /sbin/iwconfig
Virtual Private Networks
VPN
Server
Internet
Application
Server
Virtual Private Network
Point to Point Tunneling Protocol
Based on
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Point to Point Protocol (PPP)
Generic Routing Encapsulation (GRE)
IP Hdr
GRE Hdr
Encrypted
GRE Body
PPP
IP TCP
Data
 Weaknesses
 Poor Encryption
 Session handshaking done in clear
IPSec
Part of IPv6 Spec
Authentication Header (AH)
IPv4 Hdr
Auth Hdr
TCP/UDP Hdr & Data
 Encapsulating Security Payload (ESP)
IPv4 Hdr
ESP Hdr
Encrypted
TCP Hdr
DataPayload
ESP Tlr
 Modes: Transport and Tunnel
ESP Auth